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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>

    <script>
        
        //var 声明的变量往往会越作用域(越域)
        //let 声明的变量有严格局部作用域

        {
            var a = '1111会越域';
            let b =2;

        }
        console.log(a);
        //console.log(b); //let.html:22 Uncaught ReferenceError: b is not defined

        //var 可以声明多次
        //let 只能声明一次

        var m =1;
        var m =2;
        var m =3;

        //let n =3;
        let n =4;

        console.log(m) //2
        console.log(n) //let只能声明一次 Uncaught SyntaxError: Identifier 'n' has already been declared


        //var 会变量提升
        //let 不存在变量提升

        console.log(x) //Uncaught ReferenceError: x is not defined
        var x =10
        console.log(y) //Uncaught ReferenceError: y is not defined
        var y =20
        










    </script>
    
</body>
</html>